The present invention relates generally to metallurgy, and more particularly to a method for metallurgically attaching together two tubes.
Resistance welding (also known as electric-resistance welding) is a known metallurgical process wherein metal is heated by its own resistance to a semi-fused (i.e., soft) or fused (i.e., molten) state by the passage of very heavy electric currents for very short lengths of time and then welded by the application of pressure.
Conventional methods for attaching parts together include gas metal arc welding. Gas metal arc welding uses a consumable metal wire as one electrode and the parts as another electrode, and moves the consumable metal wire (or the parts) to draw an arc and weld the parts together. The welding is accompanied by a gas (such as a mixture of argon and carbon dioxide) to prevent oxidation and stabilize the arc. Such gas metal arc welding is well known. In a conventional gas metal arc welding technique, solid metal wire or metal core wire (i.e., an annular-solid wire whose core is filled with metal powder such as a mixture of metal, alloy and/or oxide powders) is used with the wire at a positive electrical welding potential and with the parts electrically grounded. The welding arc creates a molten weld puddle which results in the welding together of the parts. A ceramic ferrule is used to contain the weld puddle when needed. Gas metal arc welding requires expensive welding equipment, the molten weld puddle tends to flow away from the joint area resulting in welds of inconsistent quality, and the process requires a long cycle time between welds.
Conventional methods for attaching parts together also include friction welding. To join two tubes together end to end, one of the tubes is rotated about its longitudinal axis, and the tube ends are pressed together, wherein friction causes heating of the ends creating the weld. To join a tube to a plate, the tube is rotated about its longitudinal axis, and the tube end and the plate are pressed together, wherein friction causes heating creating the weld. Friction welding requires expensive welding equipment, and the process requires a long cycle time between welds.
Expensive fasteners, used for attaching a member to a tube, are known which penetrate the near and far wall portions of the tube, which have a varying cross-section, shoulders, flanges, etc. to keep the near and far wall portions from collapsing, and which are arc/projection welded at both the near and far wall portions to prevent relative motion.
What is needed is a less expensive method for metallurgically attaching together two tubes.
A first method of the invention is for metallurgically attaching together two tubes and includes steps a) through e). Step a) includes obtaining a first tube having a far wall portion with a first through hole and having a near wall portion with a second through hole. Step b) includes obtaining a second tube including a first wall portion having a first outward fold with spaced-apart first and second fold portions and including a second wall portion having a second outward fold with spaced-apart third and fourth fold portions. Step c) includes, after steps a) and b), positioning the first and second tubes with the first outward fold passed through the second through hole and contacting the far wall portion surrounding the first through hole and with the second outward fold located outside the near wall portion. Step d) includes, after step c), creating a first resistance welding current path through the first and second tubes proximate the first outward fold and the far wall portion and relatively moving the first outward fold deformingly against the far wall portion creating a first weld zone which includes at least some of the first outward fold and at least some of the far wall portion. Step e) includes, after step d), creating a second resistance welding current path through the first and second tubes proximate the second outward fold and the near wall portion and relatively moving the second outward fold deformingly against the near wall portion creating a second weld zone which includes at least some of the second outward fold and at least some of the near wall portion.
Several benefits and advantages are derived from the first method of the invention. Resistance welding is less expensive than gas metal arc welding or friction welding. Resistance welding also has a shorter cycle time between welds than gas metal arc welding or friction welding. When the second tube is a short tube having one end flush with the far wall portion and having another end flush with the near wall portion, the second tube functions as a tube stiffener for the first tube. This allows an inexpensive fastener to pass through the second tube, as can be appreciated by the artisan.